1. Field of the Invention
The present invention relates to an arrester that is used for protecting an electric apparatus from an abnormal voltage penetrating into a system in an electric power plant, a substation and the like.
2. Description of the Related Art
A polymer arrester in which an internal element including a zinc oxide element is directly molded with a polymer such as silicon rubber is provided with a mechanical strength by an insulating support member such as a glass fiber reinforced plastic (GFRP) arranged so as to surround the zinc oxide element.
Generally, an FRP in which a glass fiber is extended in one direction has an excellent mechanical strength against a tensile load or a bending load exerting in a direction perpendicular to the direction of the glass fiber. However, the mechanical strength is not high against a shear load exerting in a direction parallel to the direction of the glass fiber. Therefore, a shape of an FRP and a method of fixing electrodes arranged at both ends of a zinc oxide element and the FRP are key factors in the configuration of a polymer arrester.
In a conventional polymer arrester disclosed in Japanese Patent Application Laid-open No. 2003-297609, an FRP and electrodes are fixed by fitting the FRP, provided with wide portions each having a substantially isosceles triangular or circular shape provided at both end portions thereof, into the electrodes each having a groove of the same shape (substantially isosceles triangular or circular shape) as that of each of the wide portions of the FRP, and the FRP is prevented from falling off by each of the wide portions of the FRP being hooked into each of the grooves of the electrodes.
However, with the configuration of the polymer arrester disclosed in Japanese Patent Application Laid-open No. 2003-297609, when a bending load is applied to the arrester, a bending stress is generated in the base of the wide portion of the FRP, and when a tensile load is applied to the arrester, a shear stress is generated in the wide portion of the FRP.
Therefore, in the conventional configuration, in order to improve the mechanical strength against the bending load, it is required to increase the width of the FRP when the thickness of the FRP is kept constant. Further, in order to improve the mechanical strength against the tensile load, it is required to increase the dimension of the wide portion. Therefore, in either case, the sizes of the FRP and the electrode are increased. In addition, when the dimension of the wide portion is increased, there is another problem that it is not cost effective because a processing portion of the FRP is increased.